The present invention relates to a sensor mounting bracket, in particular a sensor mounting bracket for a load cell. The present invention also relates to a mounting bracket for a sensor comprising a symmetrical mounting arrangement capable of mounting effect amelioration. The invention further relates to a weigh scale system comprising a sensor mounting bracket and a sensor comprising a symmetrical mounting arrangement.
Typically sensors such as load cells are mounted to a support structure in a weigh scale system or to a reinforced part directly attached to it in an installation. The sensor is attached in at least two places when it is a load cell for sensing force. A loading fixture is mounted directly to the load cell at another location on it. Typically, the load cell is mounted to the support structure at its bottom or to one or more of its sides at one end of the load cell in a scale system. The loading fixture is mounted at the top or to one or more sides of the opposite end of the load cell. The load cell, and hence the sensor, is made stiff at these ends to reduce distortion from so-called mounting effects.
The so-called “mounting effect” can be seen as a result of mounting the sensor on the adjacent support structure and/or of mounting the loading fixture on the sensor. Fasteners, for example bolts, attaching the sensor to the attachments distort the sensor and cause output changes that are undetermined and that change with changes in load and temperature and even time and usage.
These mounting effects can be partially compensated for when the sensor is calibrated to make the sensor as accurate as possible in that configuration. However, the compensation is limited to lower accuracy sensors with poorer resolution, since these effects are undetermined and caused by unstable frictional joints that can change.
The mounting effects are only reduced by using stiffening members and through calibration of the scale system incorporating the sensor. As a result, the performance of the sensor is compromised. Particularly, for sensors wherein a lower resolution and accuracy is required, for example when between 500 to 10,000 unit divisions is required, controlling the stiffness of the sensors at attachments areas may be deemed to be adequate. However, the desire to have higher resolution and accuracy, for example when between 25,000 and 100,000 unit divisions is required, as is the case for example in part counters and pharmaceutical scales, requires an improved solution than the reduction of the mounting effects seen as a result of controlling the stiffness of the sensor at attachment areas.
Furthermore, distortion from loading and temperature in the support structure at the fixed portion of the sensor may be different than that in the loading fixture at the live portion for load cells and not enable improved symmetry in bending of the end blocks. As a result, scale systems require calibration after assembly to be accurate.